Hot Rod Deluxe no More Drive

[drewl]

So, this HR Deluxe will switch to the yellow channel, but not the red More Drive.
TP36 stays -16v, instead of switching to +16v
TP35 is a little low
TP34 doesn't change

Is it possible the LED could be funky?
With yellow channel selected, it has a bit of red to it.
When I break the link to it by lifting one side of R84 the More Drive circuit switches as it's supposed to.

I have already swapped out U3, Q3 and Q4and CR23 and 24

Thanks


hotrod_deluxe.pdf

[Jazz P Bass]

A faulty led has been known to cause switching issues as it is a part of the circuit.

Fender no longer supplies the bi color led.

Did a search at Mouser and found these: https://www.mouser.com/Optoelectroni...1bc8?P=1z0jdq1

[drewl]

Thanks.
I know I have some dual LED's, we'll see if they work the same.

[nevetslab]

Is this WITH the foot switch or without? Assuming either way, the conditions remain....almost sounds like there's an open trace, as all-too-often happen on the Hot Rod series PCB's. I hate it when physics stops working on my bench like this. Have you checked the solder joints on the Foot Switch jack? The voltage potentials from the 39VAC source need those local two switches, as well as the pedal if plugged in to influence CR23 & CR24 to make it all switch. I always find solder joint issues on the panel mount jacks over time.

[drewl]

All the joints look good for that part of the circuit.
And it's the same with a footswitch or panel switches.

I am going to replace the jacks as the threads are stripped on all of them.

[drewl]

Well the two dual LED's behaved the same as the stock one.
so I started playing with the value of R84.
With a 1k instead of 130, it drives the relay and activates the More Drive circuit.

Why?
Don't know.
I double checked every component in the switching circuit, everything tested fine.

[nevetslab]

Looking at the Max Output Voltage Swing graph on the 4560 Op Amp, the curve shows around 12V at 130 ohms, and 25.5V at 1k. Not sure what the voltage is across R104 (270 ohms from the two relay coils to LD1 LED). I've never run into this one before. Other than R97 (from the VAC source), all the circuit values are the same between the Hot Rod Deluxe and Hot Rod DeVille, though different values in the Test Point voltage chart..

[glebert]

Do you have a scope? Have you verified that the 39_VAC supply is healthy? With no footswitch, the panel switches for channel and drive should take that large AC voltage and chop the top and bottom halfs of the waveform when they are engaged, down to something like a volt. Does that happen?

[drewl]

Yes, yes it does.

[glebert]

When you say TP35 voltages are "a little low" does that mean more negative than spec, or smaller negative number (i.e. closer to zero)? It seems to me like your problem is in that area. Giving actual voltages rather than subjective descriptions would probably help. Similarly for TP34 is the voltage what is called out on the schematic?

[drewl]

TP34 doesn't drop below -10v

[glebert]

TP34 doesn't drop below -10v

When you say "below" a negative number that is still unclear what you mean. Actual numbers would be helpful. Schematic says it should be -13.0V for normal mode, -5.46V for drive mode, -4.36 for more drive.

[drewl]

Voltage goes from -13 in normal mode to -10v instead of going to -5.46 or -4.36 when switching to yellow and red channels.
it does not go more positive or less negative than -10v.

[glebert]

Voltage goes from -13 in normal mode to -10v instead of going to -5.46 or -4.36 when switching to yellow and red channels.
it does not go more positive or less negative than -10v.

And what are the TP35 voltages?

[nevetslab]

Voltage goes from -13 in normal mode to -10v instead of going to -5.46 or -4.36 when switching to yellow and red channels.
it does not go more positive or less negative than -10v.

So, we're seeing the result of having changed R84 from the normal 130 ohms to 1k, if that is where you left it? New uncharted territory for us. I wonder what happens under low AC line conditions? I've never checked the nominal-behaving Hot Rod Deluxe or Deville in their test-points under low-line conditions.